I had a quick look at Molten Drums' manual, and it doesn't mention supporting Audiobus, so I don't think it will work that way. It does say it supports Audio Copy/Paste, so you can use that method to paste your finished patterns into Auria.

I think the manual must out of date, I'm using it with no problem as input on Audiobus and with Auria in output. First open Audiobus then Molton and then Auria, then goto Auria input matrix and choose Audiobus top right and choose which track you want to record on and it will appear ready to record, the track will arm itself.

Then in that case a normal Audiobus setup should probably work, probably nothing in the MIDI prefs need to be setup. Just open Audiobus, put Molten Drums in the Input (left-hand) slot and Auria in the Output (right-hand) slot. Auria should automatically create a new track and route it from Audiobus.